Natural gas has received much attention as a plentiful and viable alternative to traditional fuels such as diesel. Natural gas, however, has a lower energy density than traditional fuels such as diesel and gasoline. As a result, mobile machines generally use liquefied natural gas (“LNG”) as fuel. To maintain natural gas in liquid form at atmospheric pressure, its temperature must remain below about −160° C. Mobile machines utilizing LNG as a fuel, therefore, typically store LNG in insulated tanks. Some heat can still enter the tank because of imperfect insulation, causing some of the LNG to change its state to a gaseous form.
The gaseous fuel (“boil-off”) accumulates near the upper portions of the tank. Moreover, as the amount of gaseous fuel produced in the tank increases, the pressure within the tank also increases. The increasing pressure, if left unchecked, can damage the tank and can even cause the tank to explode. Traditional LNG systems, therefore, vent the gaseous fuel (composed mostly of methane) directly to the atmosphere. Government regulations, however, no longer permit direct venting of gaseous fuel to the atmosphere because it contributes to greenhouse gas (GHG) emissions. To get around this problem, some LNG systems ignite the gaseous fuel as it vents to atmosphere, thus reducing the amount of methane leaving the tank. Although effective, this process results in an inefficient waste of potential fuel energy.
One attempt to address the problems described above is disclosed in Japanese Patent No. JP 2009216078 of Masataka et al. that issued on Sep. 24, 2009 (“the '078 patent”). In particular, the '078 patent discloses a canister containing an adsorbent material to adsorb fuel vapors generated in a fuel tank. The '078 patent further discloses a vortex tube, which receives a supply of compressed air at an inlet and separates the compressed air into a hot stream of air and a cold stream of air. The system of the '078 patent directs the cold air stream towards the fuel tank, cooling the fuel tank, and reducing the amount of fuel vapor produced in the tank. Simultaneously, the system of the '078 patent directs the hot air stream towards the canister to help segregate the adsorbed fuel from the adsorbent material and introduces the segregated fuel into the suction passage of an engine. The '078 patent also discloses that at least a portion of the gaseous fuel formed in the fuel tank is discharged to the atmosphere.
Although the '078 patent discloses a method for partial recovery of fuel vapor generated in a fuel tank, the system of the '078 patent requires an adsorbent material to adsorb and release the fuel vapor generated in the fuel tank. Moreover, the '078 patent requires an external source of compressed air to generate the required hot and cold streams of air. The adsorbent material and external source of compressed air add complexity and make the system of the '078 patent more expensive. Further, although the system of the '078 patent consumes some of the fuel vapor by using it in the engine, the system of the '078 patent also discharges some fuel vapor into the atmosphere contributing to GHG emissions.
The fuel recovery system of the present disclosure solves one or more of the problems set forth above and/or other problems in the art.